1. Field of the Invention
This invention relates to a method of extracting soluble products from materials containing or composed of biological matter or organic matter using microwave energy and apparatus therefor.
2. Description of the Prior Art
Various microwave advances have been documented where e.g. grains containing fats and oils have been dried by microwave heating, followed by steps to remove husks and to extract oils, e.g. U.S. Pat. No. 4,464,402, Gannon. Grains and seeds also have been microwave treated to heat the extracted medium, e.g. Ganzler and Salgo, 1987, Z. Lebensm Unters Forsch 184: 274-276. In these experiments, radiation was primarily employed to heat the extractant medium.
Microwave drying of food products followed by subsequent solvent extraction is disclosed in U.S. Pat. No. 4,554,132 by Collins, but with no extraction process.
British 1,209,675 discloses inactivating enzymes of palm fruits with microwave radiation, followed by solvent extraction of palm oil.
Heitkamp et al., Canadian 987,993, describes a microwave induced migration of flavour and aroma constituents towards the surface in certain tissue such as tobacco or tea in the presence of moisture and optionally a solvent. Heitkamp does not teach any enhanced extraction of the flavour or aroma constituents into the extracted medium.
Additionally, Craveiro et al. in the Flavour and Fragrance Journal 4, 1989: 43-44, discuss the production of volatile material from plant material exposed to microwave energy in an air stream.
Ganzler, Salgo, and Valko in Journal of Chromatography, 371, 1986: 299-306, disclose microwave sample preparation for organophosphate pesticides, antinutritives and crude fat samples. Dried sample materials are milled to the point of particulation and suspended in an organic medium. The Ganzler et al. method describes an extraction in which the glandular and vascular matter of the dried sample material is destroyed mechanically prior to microwave treatment; this causes a loss of volatile oils and allows for undesirable materials to be obtained. That method calls for a long centrifugation time, a well-known extraction technique. In addition, the method indicates that the suspensions of samples and solvents are cooled and subsequently re-exposed to microwaves. Thus, heating of the extraction environment occurs with no recovery of the extractant or any volatile oils.
Steam distillation and solvent extraction methods are well known in the art but are limited by high temperatures, as well as being dangerous when using certain organic solvents and being deficient in producing an uncontaminated product.
Accordingly, there is a need for an extraction method and apparatus for producing maximum yields and recovery of volatile oils and other useful substances contained in cellular biological material by microwave inducement without any of the disadvantages and inherent limitations of the prior art.